Method and means for allocating time slots in a TDD system

ABSTRACT

Method and apparatus for allocating time slots in a time division duplex communication system. First and second types of time slots selected from receiving and transmitting type time slots are allocated as the first and second time slots, respectively, in a current frame. Based on an amount of information to be transferred, it is determined whether at least one time slot following the second time slot of the frame should be allocated as the first type of time slot, and if so, the last time slot of the frame is always allocated as the first type of time slot, whereby the last time slot of the frame and the first time slot of a succeeding frame are of the same type. If an additional time slot(s) is allocated for the second type of time slot, the third slot is always designated for the second type.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and a means for allocatingtime slots in a time division duplex communication system. Particularly,the method and the means for allocating time slots according to thepresent invention can be implemented in communication units of a timedivision duplex communication system, e.g. a base station and/or amobile station of a telecommunication system.

2. Description of Related Art

In a time division duplex communication system, examples of which arethe GSM-standard for outdoor mobile communication or the DECT-standardfor indoor mobile telephone communication, the receiving and thetransmitting channels are separated on a time basis. E.g. in theDECT-standard, the information is transmitted in time frames of a lengthof 10 ms having 24 time slots. The first 12 time slots are used for thedownlink connection, that is the transmission of data from a basestation to a mobile station. The last 12 time slots are used for theuplink connection, that is for the transmission of data from a mobilestation to the base station. In the GSM-standard, a combination of afrequency division duplex and a time division duplex is used. Theinformation is transmitted in time frames having 8 time slots, wherebythe uplink connection is provided in a lower frequency band and thedownlink connection is provided in a higher frequency band. Each of the8 time slots in each frame is assigned to a different mobile station.Thereby, the time slots assigned to a certain mobile station within adownlink time frame are separated from the time slots assigned to thesame mobile station in the uplink time frame by two time slots. In otherwords, if e.g. the first time slot in a downlink time frame is assignedto a certain mobile station, the fourth time slot in an uplink timeframe is assigned to the same mobile station. The time basis separationof the uplink and downlink time slots enables the construction of themobile stations to be made more simple, since the reception and thetransmission of data does not take place simultaneously.

Since in telecommunication systems as e.g. the GSM-system the datatransfer rate is restricted, attempts have been made to increase thedata transfer rate by allocating more than one time slot per frame to acertain mobile station. In JP 05153033-A such a TD digital mobiletelecommunication system is disclosed, in which the same frequency fortransmitting and receiving information is used. 1 to N time slots withinone uplink time fame are allocated to one mobile station and 1 to N timeslots within one downlink time frame are allocated to one mobile stationdepending on the information volume to be transferred between the mobilestation and a base station. Each frame is allocated either to the uplinktransfer of data or the downlink transfer of data. The uplink timeframes cannot be used for a downlink transfer of data, so that a strongasymmetric transmission of information with a large difference betweenthe amount of uplink data and the amount of downlink data is notpossible.

In JP 07107546-A, a TDMA radio communication system is disclosed, inwhich the ratio between the number of uplink and downlink time slotswithin one time frame or one super frame consisting of several timeframes is changed according to the total amount of traffic between abase station and mobile stations. In case of fast changing data transferamounts, the switching point within each frame between the uplink timeslots and the downlink time slots often changes position. Every changeof such a switching point requires a reallocation of several time slotsfor the different connected mobile stations. This known system thereforerequires a complicated circuitry.

SUMMARY OF THE INVENTION

The slot allocation method disclosed in EP 654916-A2 suffers from thesame problems.

The object of the present invention is therefore to provide a method andmeans for allocating time slots in a time division duplex communicationsystem, which allow a simple and efficient time slot allocation forvarying transfer information amounts.

This object is achieved by a method for allocating time slots accordingto claim 1 and a means for allocating time slots according to claim 8.Advantageous features of the present invention are defined in therespective subclaims.

The present invention relates to a method for allocating time slots in atime division duplex communication system, in which the information istransmitted in predetermined time frames having a predetermined numberof time slots. In a GSM-system, the number of time slots per time frameis 8. Each time frame comprises a fixed block of one receiving time slotand one transmitting time slot being adjacent to each other. For thecase where the method according to the present invention is implementedin a communication unit as e.g. a mobile station, the receiving timeslot is a downlink time slot and the transmitting time slot is an uplinktime slot. The method for allocating time slots according to the presentinvention comprises the step of allocating at least the time slotadjacent to the receiving time slot as additional receiving time slotand at least the time slot adjacent to the transmitting time slot asadditional transmitting time slot dependent on an amount of informationto be transferred. Thus, starting from the fixed block consisting of thereceiving and the transmitting time slot, the time slots for receivingand transmitting are extended, whereby additional receiving time slotsare added on the side of the receiving time slot of the fixed block andadditional transmitting time slots are added on the side of thetransmitting time, slot of the fixed block. Thereby, the additional timeslots can be added or additionally allocated crossing the border of twoadjacent time frames. In other words, the additional time slots can beextended from one time frame into an adjacent time frame.

Thus, even if a big difference between the uplink data amount and thedownlink data amount occurs, the method and the means according to thepresent invention provides an efficient and simple possibility totransfer the information to be transferred asymmetrically. Since theposition of the switching point between the receiving time slot and thetransmitting time slot is fixed due to the fixed block position, themethod according to the present invention allows a transfer data amountchange of a certain mobile station without the need of a reallocation oftime slots for other mobile stations. Thus, the present invention isparticularly advantageous in a multiple access communication system, inwhich one time frame is assigned to several communication units, e.g.several mobile stations.

Advantageously, the number of additional receiving time slots and thenumber of additional transmitting time slots are independent from eachother. This means, that data or information can be transferredasymmetrically between two communication units. The receiving and thetransmitting time slot of the fixed block can be allocated to a commonfirst communication unit, e.g. a mobile station, whereby thetransmitting time slot precedes or is earlier than the receiving timeslot. In other words, the transmitting time slot is positioned in frontof the receiving time slot on the time axis, so that problems in view ofthe timing advance can be provided. The timing advance means, that thebase station has to receive an uplink time slot at a correct timing. Tomeet this requirement, the transmitting timing of the uplink time slotis adjusted e.g. by a mobile station taking the propagation delay intoconsideration. Of course, the propagation delay is more important inoutdoor environments, in which communication units as e.g. mobilestations are sometimes moved with high speed or in which multipatheffects occur. The adjustment of the transmission timing of the uplinktime slot is called timing advance. Here, the method of the presentinvention is implemented in a mobile station and if the transmittingtime slot is earlier than the receiving time slot, the transmissiontiming of the uplink time slot transmitted from the mobile station tothe station is not necessary, since the timing advance does not play arole in this case.

The additional time slots can either be allocated to the same firstcommunication unit as the fixed block, or, in case of a multiple accesscommunication system, one time frame is assigned to severalcommunication units and the additional time slots are allocated tocommunication units different from said first communication unit. Evenin a multiple access communication system, the present inventionprovides an advantageous possibility for an asymmetric data transfer.

The above-mentioned timing advance only becomes important, if all thetime slots of a time frame are used for data transfer. Even in case thatthe transmitting time slot is preceding the receiving time slot, in oneposition of the time frame another switching point between atransmitting time slot and a receiving time slot occurs. In thisswitching point, a receiving time slot is preceding a transmitting timeslot, so that, e.g. in a mobile station, the timing advance leads to apossible overlap of the earlier receiving time slot into the latertransmitting time slot. In this case, a guard period can be provided inat least one of the adjacent time slots. In other words, a guard periodcan be provided either in the earlier receiving time slot or in thelater transmitting time slot to avoid problems due to the timingadvance. Advantageously, the guard period is only provided at the end ofthe receiving time slot.

According to claim 8, a means for allocating time slots in a timedivision duplex communication system is provided, in which theinformation is transmitted in predetermined time frames having apredetermined number of time slots. Each time frame comprises a fixedblock of one receiving time slot and one transmitting time slot beingadjacent to each other. Said means for allocating time slots allocatesat least the time slot adjacent to the receiving time slot as additionalreceiving time slot and at least time slot adjacent to the transmittingtime slot as additional transmitting time slot dependent on an amount ofinformation to be transferred. Said means for allocating time slotsaccording to the present invention can e.g. be implemented in acommunication unit of a telecommunication system, as a mobile stationand/or a base station. All statements above made in reference to themethod for allocating time slots according to the present invention areidentically true for the means for allocating time slots according tothe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following description, preferred embodiments of the presentinvention are explained relating to the accompanying drawings, in which

FIG. 1 shows an example of a fixed block comprising one receiving timeslot and one transmitting time slot being located at the beginning ofrespective time frames,

FIG. 2.shows some time frames with additional transmitting time slotsand additional receiving time slots,

FIG. 3 shows some other time frames, wherein one of the time frames issaturated with data to be transmitted or received, so that an additionalswitching point is present.

FIG. 4 shows an enlarged section of FIG. 3 showing a timing advance ofan additional transmitting time slot adjacent to a preceding receivingtime slot, and

FIG. 5 shows a schematic example of a communication unit comprising ameans for allocating time slots according to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

In FIG. 1, three time frame F₁, F₂ and F₃ are schematically shown. Eachframe contains e.g. eight time slots, as in a GSM-system. Although alltime frames shown in FIGS. 1, 2 and 3 comprise eight time slots, thepresent invention is not limited to this case and the time frames cancomprise any other required number of time slots. In each frame, thefirst two time slots 1 and 2 build a fixed block comprising atransmitting time slot 1 and a receiving time slot 2. In case that thepresent invention is implemented e.g. in a mobile station of atelecommunication system, the transmitting time slot is an uplink timeslot for transmitting data or information from the mobile station to abase station, and the receiving time slot 2 is a downlink time slot fortransmitting data from the base station to the mobile station. Thetransmitting time slot 1 and the receiving time slot 2 are thus assignedto a certain pair of communication units, e.g. a base station and amobile station. The base station can thereby be part of the multipleaccess communication system, in which one frame is assigned to severalmobile stations. The fixed block comprising the transmitting time slot 1and the receiving time slot 2, however, is always on a fixed position.

In the first and second frame F₁ and F₂ shown in FIG. 1, the sixremaining time slots 3 to 8 in each frame are not used for transferringinformation. Since the transmitting time slot 1 is placed in advance ofthe receiving time slot 2, this slot allocation can cope with timingadvance as explained above. For a base station, the timing advance isadjusted by adjusting the timing of the time slot transmitted from thebase station to the mobile station.

In the example shown in FIG. 1, the first frame F₁, the next frame F₂and the third frame F₃ are not saturated since only the transmittingtime slot 1 and the transmitting time slot 2 of the fixed block are usedto transfer information in each of the frames. The last time slot 8 ofthe third frame F₃ is an additional transmitting time slot of the fixedblock of the fourth frame F₄ of FIG. 4.

In FIG. 2, information are transmitted in the transmitting time slot 1and the receiving time slot 2 forming a fixed block in each of the shownframes F₄, F₅ and F₆, as in the first example shown in FIG. 1. However,since there is more information to send and to receive, an additionaltransmitting time slot 8 is added before the time slot 1 of the fixedblock in the time axis direction. Additional receiving time slots 3 and4 are added behind the receiving time slot 2 in the time axis direction.Thus, an increased amount of information or data can be transferredbetween a mobile station and a base station or between several mobilestations and one base station. In the later case, the additionaltransmitting and/or receiving time slots can be allocated to differentmobile stations. For example in the fifth time frame F₅, the additionalreceiving time slots 3, 4, 5 can be allocated to one or more differentmobile stations. The position of the basic block, however, remainsunchanged, so that the switching point between transmitting andreceiving information, which is located between the first time slot 1and the second time slot 2 in each frame, remains on the same position.This switching point is the only switching point, since the time framesare not saturated with information to be transferred. As can be seenfrom FIG. 2, according to the present invention, the number ofadditional transmitting time slots and additional receiving time slotscan be increased independently, so that an asymmetric transmission ofdata is possible. In case of a multiple access communication system, inwhich one time frame is assigned to several mobile stations, theadditional time slots can be allocated to one or more different mobilestations. For a certain mobile station, the time slots to be transmittedor received may not come in a regular interval. However, the pattern ofthe slot allocation is maintained and continued over at least severalframes, e.g. two frames F₁ and F₂ as shown in FIG. 1. In FIG. 2, theslot allocation pattern changes for the succeeding frames F₄, F₅ and F₆.The pattern of the slot allocation is advantageously not changed frameby frame, but is changed only, when the required data amount to betransferred is changed. This is the case for the time frame shown inFIG. 2, in which the data amount to be transferred is reduced to onetransmitting time slot from frame F₄ to frame F₅ and the receiving timeslot 2 from frame F₅ to frame F₆.

In case of a multiple access communication system, in which differenttime slots are assigned to different mobile stations, the time slots 3and 4 being used as additional receiving time slots and the time slot 8being used as additional transmitting time slot in the time frame F₄ canbe assigned to a second mobile station, when the transmitting time slot1 and the receiving time slot 2 of the fixed block are assigned to afirst mobile station. The time slots 3 and 4 can also be allocated to asecond mobile station and a third mobile station, respectively.

In case that the amount of information to be transferred is furtherincreased, the maximum information transfer rate can be achieved byusing all the time slots in each time frame for transferring data, asshown in FIG. 3 for the time frame F₇. In the shown example, thetransmitting time slot 1 and the receiving time slot 2 are still ontheir fixed position at the beginning of each time frame. The time slots3 to 7 of the frame F₇ are used as additional receiving time slots.Thereby, the different time slots 3 to 7 can be assigned or allocated todifferent mobile stations. An additional transmitting time slot 8 isalso used in the time frame F₇, so that the last additional receivingtime slot 7 and the succeeding additional transmitting time slot 8 areadjacent to each other. If in this situation the base station is locatedclose to the mobile station, so that the propagation delay is small,there is no serious problem. If, however, the base station is locatedfar from the mobile station, e.g. a few kilometer, the mobile stationhas to transmit the transmitting time slot 8 in advance to compensatefor the propagation delay. In other words, a timing advance isnecessary. Therefore, the mobile station has less time to receive thelast additional receiving time slot 7. This situation is shown in moredetail in FIG. 4. FIG. 4 shows a section of FIG. 3 with the lastadditional receiving time slot 7 and the additional transmitting timeslot 8 of the preceding frame F₇ as well as the transmitting time slot 1of the succeeding time frame F₈. As can be seen from FIG. 4, the lastportion of the receiving time slot 7 is emptimed and used as a guardperiod to enable an earlier transmission of the additional transmittingtime slot 8. It has to be understood, that the timing advance problemonly occurs, when a receiving time slot and a succeeding transmittingtime slot are adjacent to each other, which are assigned to the samemobile station. It is therefore advantageous, not to allocate successivetransmitting and receiving time slots to one mobile station in thiscase.

In time frame F₈ following time frame F₇ with the maximum informationtransfer, the amount of information to be transferred is reduced andonly the time slots 3, 4 and 5 are allocated as additional receivingtime slots. In the following time frame F₉, the amount of information tobe transferred is further reduced to the basic block comprising thetransmitting time slot 1 and the receiving time slot 2.

In FIG. 5, a communication unit 10, in which the present invention isincorporated or implemented, is schematically shown. The communicationunit 10 can e.g. be a mobile station or a base station of a mobiletelecommunication system.

The communication unit 10 comprises an antenna 11, through whichinformation modulated onto respective carrier frequencies can betransmitted and received. The communication unit 10 comprises areceiving means 12, which receives incoming information through theantenna 11 and supplies the received information to a control unit 13,in which the received information are demodulated, decoded, etc. in aknown manner. The control unit 13 comprises an allocation means 15, inwhich the time slots of the predetermined time frames are allocateddepending on the amount of information to be transferred as receiving ortransmitting time slots according to the method explained above. Thecontrol unit 13 can thus also comprise a means for determining theamount of information to be transferred, i.e. received or transmitted togive corresponding information to the allocation means 15, so that theallocation means 15 correspondingly allocates the time slots asreceiving or transmitting time slots depending on the amount of transferinformation. The allocation means 15 of the control unit 13 allocatesthe time slots according to the slot allocation method explained abovein relation to FIGS. 1 to 4. Thereafter, the control unit 13 provides atransmission means 14 with corresponding information to be transmittedwithin the correspondingly allocated time slots by means of the antenna11 to another communication unit. The control unit 13 can furthercomprise a guard period means 16, which, in case that an additionalreceiving time slot and an additional transmitting time slot becomeadjacent to each other, e.g. in the case shown in FIGS. 3 and 4,provides a guard period in at least one of said adjacent additional timeslots. As stated above, this situation becomes only relevant in the casethat the preceding receiving time slot and the succeeding transmittingtime slot are assigned to the same communication unit 10. In this caseit is advantageous, if the guard period means 16 provides said guardperiod at the end of said additional receiving time slots, e.g. theadditional receiving time slot 7 of time frame F₇ shown in FIGS. 3 and4.

1. Method of allocating time slots in a time division duplexcommunication system, in which information is transmitted and receivedin predetermined time frames each having a predetermined number of timeslots, wherein first and second types of time slots selected fromreceiving and transmitting type time slots are allocated, the first timeslot of each frame is allocated as the first type of time slot, and thesecond time slot of each frame is allocated as the second type of timeslot, said method comprising: determining, based on an amount ofinformation to be transferred, whether at least one time slot followingthe second time slot of a current frame should be allocated as the firsttype of time slot, and if so, always allocating the last time slot ofthe current frame as the first type of time slot, whereby the last timeslot of the current frame and the first time slot of a succeeding frameare the same type of time slots; and allocating time slots following thesecond time slot of the current frame as additional receiving ortransmitting time slots dependent on an amount of information to betransmitted and/or received, wherein if additional time slot(s) areallocated for the second type of time slot, always allocating at leastthe third time slot of the current frame as an additional second typetime slot.
 2. The method according to claim 1, wherein the number ofadditional receiving time slots and the number of additionaltransmitting time slots are independent from one another.
 3. The methodaccording to the claim 1, wherein the first and second time slots of thecurrent frame are receiving and transmitting time slots, respectively,and each is allocated to a first communication unit.
 4. The methodaccording to claim 3, wherein additional slots are also allocated to thefirst communication unit.
 5. The method according to claim 3, whereinone of time frames (F₁, F₂, . . . ) is assigned to several communicationunits and the additional time slots are allocated to communication unitsdifferent from said first communication unit.
 6. The method according toclaim 1, wherein when both the last time slot and next to last time slotof the current frame are each allocated for transmitting or receiving, aguard period is provided in at least one of said last and next to lasttime slots.
 7. The method according to claim 6, wherein said next tolast time slot of the current frame is the second type of time slot,said last time slot is the first type of time slot, and said guardperiod is provided at the end of said next to the last time slot. 8.Apparatus for allocating time slots in a time division duplexcommunication system, in which information is transmitted and receivedin predetermined time frames each having a predetermined number of timeslots, wherein first and second types of time slots selected fromreceiving and transmitting type time slots are allocated, the first timeslot of each frame is allocated as the first type of time slot, and thesecond time slot of each frame is allocated as the second type of timeslot, said apparatus comprising: determining means for determining,based on an amount of information to be transferred, whether at leastone time slot following the second time slot of a current frame shouldbe allocated as the first type of time slot, and if so, alwaysallocating the last time slot of the current frame as the first type oftime slot, whereby the last time slot of the current frame and the firsttime slot of a succeeding frame are the same type of time slots; andallocating means for allocating time slots following the second timeslot of the current frame as additional receiving or transmitting timeslots dependent on an amount of information to be transmitted and/orreceived, wherein if additional time slot(s) are allocated for thesecond type of time slot, always allocating at least the third time slotof the current frame as an additional second type time slot. 9.Apparatus according to claim 8, wherein the number of additionalreceiving time slots and the number of additional transmitting timeslots are independent from one another.
 10. Apparatus according to claim8, wherein the first and second time slots of the current frame arereceiving and transmitting time slots, respectively, and each isallocated to a first communication unit.
 11. Apparatus according toclaim 10, wherein additional slots are also allocated to the firstcommunication unit.
 12. Apparatus according to claim 10, wherein one oftime frames (F₁, F₂, . . . ) is assigned to several communication unitsand the additional time slots are allocated to communication unitsdifferent from said first communication unit.
 13. Apparatus according toclaim 8, wherein when both the last time slot and next to last time slotof the current frame are each allocated for transmitting or receiving, aguard period is provided in at least one of said last and next to lasttime slots.
 14. Apparatus according to claim 13, wherein said next tolast time slot of the current frame is the second type of time slot,said last time slot is the first type of time slot, and said guardperiod is provided at the end of said next to last time slot. 15.Communication method for transmitting and receiving information in atime division duplex communication system, comprising the steps of:allocating a changeable number of receiving time slots and a number oftransmitting time slots in a time frame having a predetermined number oftime slots, the allocation of time slots being changed when the amountof information to be transferred is changed, and transmittinginformation by using said time slots dependent on the amount ofinformation to be transferred, wherein said time frame contains at leasta receiving time slot and an adjacent transmitting time slot, and aguard period provided in at least one of said receiving and adjacenttransmitting time slots.
 16. The communication method according to claim15, wherein the number of receiving time slots and the number oftransmitting time slots are independent of each other.
 17. Thecommunication method according to claim 15, wherein in said adjacentreceiving and transmitting time slots said receiving time slot precedessaid adjacent transmitting time slot.
 18. The communication methodaccording to claim 17, wherein said guard period is provided at the endof said receiving time slot.
 19. A communication unit for transmittingand receiving information in a time division duplex communicationsystem, said information being transmitted in predetermined time frameshaving a predetermined number of time slots, comprising allocation meansfor allocating the time slots as receiving time slots and transmittingtime slots dependent on an amount of information to be transferred,whereby each time frame comprises a receiving time slot and an adjacenttransmitting time slot, determining means for determining the amount ofinformation to be transferred, whereby the allocation of time slots bythe allocation means is changed when the amount of information to betransferred is changed, and guard period means for providing a guardperiod in at least one of said receiving and adjacent transmitting timeslots.
 20. The communication unit according to claim 19, wherein thenumber of receiving time slots and the number of transmitting time slotsare independent of each other.
 21. The communication unit according toclaim 20, wherein in said adjacent receiving and transmitting timeslots, said receiving time slot precedes said adjacent transmitting timeslot.
 22. The communication unit according to claim 21, wherein saidguard period means provides said guard period at the end of saidreceiving time slot.
 23. Communication method for transmitting andreceiving information in a time division duplex communication system,comprising the steps of: allocating a predetermined number of time slotsby which said time division duplex communication system transfersinformation, said predetermined number of time slots comprising fixedblocks of a receiving time slot and an adjacent transmitting time slot,allocating at least the time slot adjacent to the receiving time slot ofa fixed block as an additional receiving time slot and at least the timeslot adjacent the transmitting time slot of said fixed block as anadditional transmitting time slot dependent on an amount of informationto be transferred, and changing the allocation of said time slots whenthe amount of information to be transferred is changed.
 24. Thecommunication method according to claim 23, wherein the number ofadditional receiving time slots and the number of additionaltransmitting time slots are independent of other.
 25. The communicationmethod according to claim 23, wherein the receiving time slot and thetransmitting time slot of the fixed block are allocated to a firstcommunication unit, and the transmitting time slot precedes thereceiving time slot.
 26. The communication method according to claim 25,wherein the additional time slots are allocated to said firstcommunication unit.
 27. The communication method according to claim 25wherein one time frame having time slots is assigned to severalcommunication units and said additional time slots in said time frameare assigned to communication units different from said firstcommunication unit.
 28. The communication method according to claim 23,wherein an additional time slot of a preceding fixed block and anadditional time slot of a succeeding fixed block are adjacent eachother, and a guard period is provided in at least one of said adjacentadditional time slots.
 29. The communication method according to claim28, wherein said additional time slot of said preceding fixed block is areceiving time slot and said additional time slot of said succeedingfixed block is a transmitting time slot, and said guard period isprovided at the end of said receiving time slot.
 30. A communicationunit for transmitting and receiving information in a time divisionduplex communication system, said information being transmitted in apredetermined number of time slots, said predetermined number of timeslots comprising a fixed block of one receiving time slot and onetransmitting time slot adjacent to each other, said communication unitcomprising: allocation means for allocating at least the time slotadjacent the receiving time slot of a fixed block as an additionalreceiving time slot and at least the time slot adjacent the transmittingtime slot of said fixed block as an additional transmitting time slotdependent on an amount of information to be transferred, and determiningmeans for determining the amount of information to be transferred,whereby the allocation of time slots by said allocation means is changedwhen the amount of information to be transferred is changed.
 31. Thecommunication unit according to claim 30, wherein the number ofadditional receiving time slots and the number of additionaltransmitting time slots are independent of each other.
 32. Thecommunication unit according to claim 30, further comprising guardperiod means for providing a guard period in at least one of adjacentadditional time slots included in a preceding fixed block or asucceeding fixed block.
 33. The communication unit according to claim32, wherein said guard period means provides said guard period at theend of an additional receiving time slot when said additional receivingtime slot precedes an additional transmitting time slot.
 34. Acommunication device for transmitting and/or receiving information intime frames having predetermined time slots in a time division duplexcommunication system, said communication device comprising: means forallocating the predetermined time slots into a number of receiving timeslots and a number of transmitting time slots; means for changing theallocation of said time slots based on an amount of information to betransferred; and means for providing a guard period between a receivingtime slot which is one of said allocated receiving time slots and asucceeding adjacent transmitting time slot which is one of saidallocated transmitting time slots.
 35. A communication method fortransmitting and/or receiving information in time frames havingpredetermined time slots in a time division duplex communication system,comprising the steps of: allocating the predetermine time slots into anumber of receiving time slots and a number of transmitting time slots;changing the allocation of said time slots based on an amount ofinformation to be transferred; and providing a guard period between areceiving time slot which is one of said allocated receiving time slotsand a succeeding adjacent transmitting time slot which is one of saidallocated transmitting time slots.